Fabricating turbine rotors composed of separate components

Abstract

A steam turbine rotor is constructed from a first forging of a first alloy, and a second forging of a second alloy different than the first alloy. For example, one of the alloys is suitable for use in a high temperature environment and the other in a low temperature environment. The forging ends are contoured so as to provide central portions, which may be disc-shaped, and the contoured portions may be in the shape of truncated cones. A first weld, such as a root weld formed by inertia, friction, or electroslag welding, joins the central portions, and the contoured portions are joined by a second weld different than the first weld, such as a submerged arc weld. This allows the rotor forgings to be joined in relatively inexpensive horizontal facilities, and reduces the demands on the welding technology required to obtain a sound root weld.

What is claimed is:  
     
       1. A steam turbine rotor comprising: 
       a first steam turbine rotor forging of a first alloy, having a first end and a first diameter;  
       a second steam turbine rotor forging of a second alloy significantly different than said first alloy having a second end and a second diameter;  
       said first and second ends contoured so as to provide first and second central portions, respectively, having third and fourth diameters, respectively, less than said first and second diameters, and first and second contoured portions, respectively, radially outward of said first and second central portions, respectively;  
       said first and second central portions joined by a first weld comprising a friction, inertia, or electroslag weld; and  
       said first and second contoured portions joined by a second weld comprising an arc weld.  
     
     
       2. A steam turbine rotor as recited in  claim 1  wherein said arc weld comprises a submerged arc weld. 
     
     
       3. A steam turbine rotor as recited in  claim 1  wherein said first alloy is a CrMo alloy, and wherein said second alloy is an NiCrMo alloy. 
     
     
       4. A steam turbine rotor as recited in  claim 1  wherein said contoured portions are truncated cones. 
     
     
       5. A steam turbine rotor as recited in  claim 4  wherein said central portions have a diameter about 20-30% of the diameter of said rotor forgings. 
     
     
       6. A steam turbine rotor as recited in  claim 5  wherein said first and second diameters are substantially the same, and said third and fourth diameters are substantially the same. 
     
     
       7. A steam turbine rotor as recited in  claim 6  wherein said first weld is not normalized or heat tempered. 
     
     
       8. A steam turbine rotor as recited in  claim 6  wherein said first alloy is a CrMoV alloy, and wherein said second alloy is an NiCrMoV alloy. 
     
     
       9. A steam turbine rotor as recited in  claim 5  wherein said central portions are disc shaped truncations of said conical contoured portions. 
     
     
       10. A steam turbine rotor as recited in  claim 9  wherein said arc weld comprises a submerged arc weld. 
     
     
       11. A method of making a steam turbine rotor from first and second steam turbine rotor forgings of different alloys having first and second ends, respectively, comprising: 
       a) forming the first and second ends so that each comprises a central portion, and a contoured portion extending axially and radially outwardly from the central portion;  
       b) bringing the central portions of the different alloy first and second steam turbine rotor forgings into aligned operative association with each other;  
       c) while the central portions are in aligned operative association with each other, welding the central portions of the first and second rotor forgings together using a first welding technique so that the first and second rotor forgings stay together and aligned during subsequent handling; and  
       d) after c), welding the contoured portions of the first and second rotor forgings together while positioned substantially horizontally using a second welding technique, different than the first technique, to form an operable composite steam turbine rotor.  
     
     
       12. A method as recited in  claim 11  wherein c) is practiced by friction, inertia, or electroslag welding. 
     
     
       13. A method as recited in  claim 12  wherein d) is practiced by arc welding. 
     
     
       14. A method as recited in  claim 11  wherein d) is practiced by submerged arc welding. 
     
     
       15. A method as recited in  claim 11  wherein the central portions of the first and second rotor forgings are substantially disc-shaped and have substantially the same diameter, and wherein b) is practiced to place the central portions in face-to-face aligned position. 
     
     
       16. A method as recited in  claim 15  wherein the contoured portions are substantially truncated cone-shaped portions and of substantially the same diameter and conic angle, and define an open volume therebetween; and wherein d) is practiced to substantially fill the open volume by arc welding. 
     
     
       17. A method as recited in  claim 11  wherein d) is practiced after c) without any intervening procedures for normalizing or heat treating the weld formed by c). 
     
     
       18. A method as recited in  claim 13  wherein d) is practiced after c) without any intervening procedures for normalizing or heat treating the weld formed by c). 
     
     
       19. A method as recited in  claim 11  further comprising using the turbine rotor so created so that the first rotor forging is disposed within a high temperature area, and the second rotor forging is disposed within a low temperature area, in a steam turbine environment. 
     
     
       20. A steam turbine rotor comprising: 
       a first steam turbine rotor forging of a first alloy, having a first end and a first diameter;  
       a second steam turbine rotor forging of a second alloy significantly different than said first alloy having a second end and a second diameter;  
       said first and second ends contoured so as to provide first and second central portions, respectively, having third and fourth diameters, respectively, less than said first and second diameters, and first and second contoured portions, respectively, radially outward of said first and second central portions, respectively;  
       said contoured portions comprising truncated cones and said central portions comprise disc shaped truncations of said conical contoured portions, and have a diameter about 20-30% of the diameter of said rotors; and  
       a first weld joining said first and second central portions, and a second weld, different than said first weld, joining said first and second contoured portions.  
     
     
       21. A steam turbine rotor as recited in  claim 20  wherein said first and second diameters are substantially the same, and said third and fourth diameters are substantially the same. 
     
     
       22. A steam turbine rotor as recited in  claim 20  wherein said first weld is not normalized or heat tempered. 
     
     
       23. A steam turbine rotor as recited in  claim 20  said first alloy is a CrMoV alloy, and wherein said second alloy is an NiCrMoV alloy. 
     
     
       24. A steam turbine rotor as recited in  claim 20  mounted for rotation, and wherein one of said rotor forgings disposed in a high temperature area, and the other of said rotor forgings disposed in a low temperature area, in a steam turbine environment.